This invention relates to a gas analyzing apparatus of the type mounted in automobiles and the like and, more particularly to a gas analyzing apparatus which may be used as a highly reliable oxygen meter, particularly as an oxygen shortage monitor.
In order to improve combustion efficiency of automobile engines and to make exhaust gases less harmful, a lean burn combustion type engine has been developed in which use is made of a lean air-fuel ratio. In such engines the weight ratio of air to fuel is higher than the theoretical air-fuel ratio of 14.7. However, oxygen sensors or air-fuel ratio meters heretofore in use for measuring the theoretical air-fuel ratio are not precise in terms of their electromotive force output when used in a lean atmosphere and therefore it is impossible for such sensors to precisely measure or detect the air-fuel ratio for a lean mixture. For this reason, various types of apparatus are installed on the intake side of a lean burn engine to keep the lean atmosphere approximately constant so as to provide good combustion control. The disadvantage of such apparatus is that this method of control not only makes the mixture control apparatus expensive but also prevents highly accurate control because of its low response speed.
Since the air-fuel ratio i.e., the weight ratio of air to fuel, can be determined by measuring the oxygen content of the mixture, gas analyzing cells constructed to measure the oxygen content through a sampling method have been proposed. The theoretical construction of such a gas analyzing cell is shown in FIG. 1. In the gas analyzing cell shown in FIG. 1, the gas to be analyzed is first introduced into a gas analyzing compartment 12 through a coupling means 10 and subsequently withdrawn from the compartment. In this case, the coupling means 10 is constructed of, for instance, an opening highly resistant to gas diffusion. Moreover, the oxygen is withdrawn by means of a partition 16 composed of an oxygen ion conductor forming part of a wall 14 of the gas analyzing compartment. The amount of electric charge required to be applied to the partition 16 for withdrawing the oxygen may be used as an index of the content of the oxygen. For this purpose, the partition 16 has a pair of electrodes 18 and 18' for detecting temperature, a pair of pressure sensing electrodes 20 and 20', and a pair of oxygen withdrawing electrodes 22 and 22'. Each of the electrodes 18, 18', 20, 20', 22 and 22' is connected by a conductor 24 to the outside of the device.
An object of the present invention is to provide a gas analyzing apparatus of the above type especially suitable for use in automobiles and having improved strength and reliability.